It is known to produce siding from thermoplastic resin materials and for this purpose extrusion techniques have been employed in accordance with which the resin material in plasticated form is extruded through a die orifice generally conforming with the cross sectional shape of the siding, after which the extruded siding is cooled to harden it. Thereafter appropriate lengths are cut from the hardened extrusion and various machining operations are applied. In operations of the kind above referred to, it is also known to utilize polyvinyl chloride resin materials, usually formulated with pigment and other constituents to impart special properties to the product.
The present invention is especially concerned with an extrusion die structure arranged to provide for equalization and increase in uniformity of flow of the plasticated resin in a region upstream of but close to the die lips, thereby minimizing tendency for the extruded siding to distort after leaving the discharge orifice of the die.
The invention also contemplates a special die structure arranged to facilitate accuracy of heating and of control of the die temperature in various localized zones, to thereby further enhance the uniformity of the extrusion.
Still further it is an object of the present invention to provide a die structure in which the plasticized material is homogenized by passage through a die passage restriction in advance of the region in which the flow is equalized, thereby providing for increase in uniformity of admixture of the various constituents of which the resin mix is made up.
The invention also has in view the provision of a die structure which will facilitate changeover from one extruded shape to another, this being accomplished without requiring complete substitution of the die, but substitution of only a portion thereof.
How the foregoing and other objects and advantages are attained will appear more fully from the following description referring to the accompanying drawings.